Ibuprofen is a well known anti-inflammatory drug. The conventional synthesis of ibuprofen involves six steps which use hazardous chemicals like sodium cyanide and the waste materials produced require downstream treatments for disposal. Recently, Hoechst Celanese Corporation developed a novel, environmentally benign, three step catalytic route for the synthesis of ibuprofen, in which carbonylation of para isobutyl phenyl ethanol is the key step. In the processes described in patented literature, the catalysts used were mainly Pd(PPh.sub.3).sub.2 Cl.sub.2 or PdCl.sub.2 or Pd(OAc).sub.2 along with excess phosphine ligands (EP 0,400,892A3, EP 0,284,310A1), which gave lower reactions rates (TOF=25-35 h.sup.-1) and lower selectivity to ibuprofen (56-69%) under mild conditions (130.degree. C., 1000 psig). Higher selectivity (&gt;95%) was obtained only at very high pressures of 2000 to 4500 psig and the rates still remained low. U.S. Pat. No. 5,536,874 and the publication J. Chem. Tech. Biotechnol, 1997, 70, 83-91, describe the carbonylation of p-IBPE in a two-phase system wherein one phase is an aqueous medium which contains a water soluble palladium complex and an acid promoter. These processes also have disadvantages such as low reaction rates (TOF=0.1 to 0.4 h.sup.-1) and lower ibuprofen selectivity (59-74%) under mild reaction conditions (90.degree. C., 450 to 900 psig).
The object of the present invention, therefore, is to provide an improved process for the preparation of ibuprofen by carbonylation of para isobutyl phenyl ethanol.